Electric sterilisers for baby feeding bottles are well-known. Such sterilisers are designed to subject the items being sterilised to a temperature of 80° to 100° for several minutes.
In a known design, the operating period is set by loading the apparatus with a predetermined amount of water which evaporates during operation of a heating element. The temperature of the heating element is monitored using a bimetallic thermal switch and when the temperature of the heating element reaches a threshold temperature, indicating that all the water has evaporated or boiled off, the thermal switch opens to cut off the supply of power to the heating element.
A problem with this design of steriliser is that effective sterilisation is dependent on the user charging it with the correct amount of water. Additionally, the effective operational time varies according to the mains voltage and the actual values and ratings of readily available components, which can have quite wide tolerances.
Another heating apparatus familiar to parents is the electric feeding bottle warmer. These devices typically consist of electrically heated bains-marie.